Repair agent and repair method for plated base, as well as plated base

ABSTRACT

Disclosed is a repair agent for a plated base including a plating layer which is disposed on a surface of a metal base and which includes a metal with a stronger tendency to ionization than metal comprising the metal base, the repair agent including a phosphoric acid compound and a phosphonic acid compound.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2016-159221 filed on Aug. 15, 2016, the entire disclosure of which is incorporated by reference herein.

BACKGROUND

The present disclosure relates to a repair agent and a repair method for a plated base which includes a plating layer disposed on a surface of a metal base, as well as to the plated base.

Zinc-plated steel sheets which are steel sheets with a zinc plating layer disposed on their surface are generally used as automobile parts. Zinc, which is included in the zinc plating layer, has a stronger tendency to ionization than iron, which is included in the steel sheets. Therefore, if the zinc plating layer suffers a scratch such that the steel sheet is exposed, the zinc plating layer offers sacrificial protection for the steel sheet as the zinc is eluted, and has the ability to form a protective film as the zinc eluted forms a film on the surface of the steel sheet exposed. Thus, the zinc plating repairs itself, and features corrosion resistance. It has been found, however, that conventional zinc plated steel sheets do not feature sufficient corrosion resistance.

Japanese Unexamined Patent Publication No. 2010-174273 discloses a corrosion-preventing film which is disposed on the surface of a metal body and which includes an underlayer comprised of electrically conductive microparticles and a surface comprised of electrically conductive macromolecules. De facto, however, even such a technique fails to provide sufficient corrosion resistance.

SUMMARY

The inventors of the present disclosure have come across yet another problem: in attempting to add a repair agent to a protective film, and trying to add all kinds of chemical compounds as single components, no sufficient corrosion resistance could be achieved.

In automotive lightweighting, steel sheets made of, e. g., high-tensile material (high-tensile steel sheets) are employed. A plated base which includes such a steel sheet having a surface covered with a plating layer is more prone to hydrogen brittleness and strength degradation caused by corrosion than a plated base including a different kind of steel sheet. This even further exacerbates the above-described problem.

The present disclosure attempts to provide a repair agent which features increased corrosion resistance.

The present disclosure relates to a repair agent for a plated base including a plating layer which is disposed on a surface of a metal base and which includes a metal with a stronger tendency to ionization than metal comprising the metal base, wherein

the repair agent includes a phosphoric acid compound and a phosphonic acid compound.

The repair agent of the present disclosure features increased corrosion resistance. More specifically, even if in an actual use environment the plated base suffers a scratch which reaches the metal base, the repair agent of the present disclosure offers such an advanced sacrificial protection and has such a remarkable ability to form a protective film that it can excellently repair itself and thus features increased corrosion resistance.

The repair agent of the present disclosure is particularly useful when the steel sheet is a high-tensile material (high-tensile steel sheet).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view which schematically shows an example plated base treated with a repair agent of the present disclosure.

FIG. 2 is a cross-sectional view which schematically shows a plated base to give an example of an embodiment in which a protective film forms on a plated base after the plated base which has been treated with the repair agent of the present disclosure has suffered a defect.

FIG. 3 is a cross-sectional view which schematically shows a plated base to give an example of an embodiment in which a protective film forms on a plated base after the plated base which has been treated with the repair agent of the present disclosure has suffered a defect.

FIG. 4 is a cross-sectional view which schematically shows a plated base to give an example of an embodiment in which the repair agent of the present disclosure is applied to a plated base which has suffered a defect, and in which a protective film forms on the plated base.

FIG. 5 is a block diagram which schematically shows a device for evaluating the repair agent of the present disclosure.

FIG. 6 shows current-potential curves of Example A1 and Comparative Examples A1, A5, A6, and A26.

FIG. 7 shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Example A1.

FIG. 8 shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A1.

FIG. 9 shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A18.

FIG. 10 shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A24.

FIG. 11 shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A28.

FIG. 12 shows an SEM photograph of a surface of a working electrode before immersion into a test fluid in the scope of Experimental Example A.

FIG. 13 shows results of having subjected a protective film on a surface of a working electrode after cathodic polarization to a thermogravimetric analysis (TGA) in the scope of Example A2 and Comparative Example A35.

FIG. 14 shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example B4.

FIG. 15 shows results of having subjected a protective film formed on a surface of a working electrode after determination of cathodic current values to an X-ray diffraction analysis (XRDA) in the scope of Example B1 and Comparative Example B4.

FIG. 16 shows current-potential curves of Comparative Examples A1 and C1.

DETAILED DESCRIPTION —Repair Agent—

A repair agent according to the present disclosure is intended for a plated base. When the plated base suffers a defect which reaches from a surface of a plating layer to a metal base of the plated base, the repair agent forms a protective film on an internal surface of the defect, in particular on a surface of the metal base which is exposed where the plated base has suffered the defect. Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that elements shown in the drawings are illustrated in a schematic and exemplary manner, and only serve the purpose of making the present disclosure comprehensible. Actual appearance and dimensions may vary from the drawings. Unless stated otherwise, the same reference characters and symbols refer to the same part or have the same meaning.

As shown in FIG. 1, a plated base 10 includes a metal base 1 and a plating layer 2 formed on a surface of the metal base 1. The metal base 1 may be any kind of base including a metal. The metal base 1 usually includes iron, and may, if so desired, include carbon, silicon, manganese, phosphorus, or sulfur. The metal base comprises 1 wt % or less (in particular 0.8 wt % or less) carbon, 0.5 wt % or less (in particular 0.3 wt % or less) silicon, manganese, phosphorus, and sulfur each, and iron (remainder).

In the field of automobile parts, it is beneficial if the metal base 1 is a steel sheet, and even more beneficial if the metal base 1 is a so-called carbon steel sheet, particularly a high-tensile steel sheet (high-tensile material).

The plating layer 2 includes as main component a metal with a stronger tendency to ionization than a metal comprising the metal base 1. Hereinafter, the metal included as the main component of the plating layer 2 and having a strong tendency to ionization is referred to as a “metal A with a strong tendency to ionization.” If the metal base 1 is a steel sheet, the metal comprising the metal base 1 is iron. As metal with a stronger tendency to ionization than iron, for example, one or more metals from a group consisting of zinc, aluminum, and magnesium may be employed. Beneficially, zinc is employed. Such a metal A with a strong tendency to ionization included in the plating layer 2 generally contributes in ionic form to a formation of a protective film, as will be described later.

In terms of the formation of the protective film on an exposed surface of the metal base 1, it is beneficial if the plating layer 2 is a zinc plating layer. A zinc plating layer is a plating layer which includes zinc. Beneficially, the zinc plating layer is a zinc alloy layer.

All kinds of processes may be employed for forming the plating layer 2. Possible processes include, for example, so-called wet-plating processes such as electroplating, electroless plating, and hot-dip plating, and so-called dry-plating processes such as vacuum plating (physical vapor deposition (PVD)), chemical vapor deposition (CVD), and mechanical plating. Beneficially, a dry-plating process, in particular mechanical plating, is employed. In the scope of mechanical plating, a plating layer (film) is formed by projecting composite particles onto an object (metal base 1) subjected to the mechanical plating. The composite particles have a core (e.g., an iron core) which has an outer shell including constituent metal particles of the plating layer. FIG. 1 is a schematic cross-sectional view of a plated base on which the plating layer 2 has been formed by mechanical plating. In an internal portion of the plating layer 2, constituent metal particles 21 have boundary surfaces and gaps. Alternatively, the plating layer may be formed in a different manner such that the constituent metal particles do not have the boundary surfaces and the gaps.

The plating layer 2 is not particularly limited in its thickness, and may be, e.g., 1 μm thick or thicker. The plating layer 2 generally has a thickness of 1 to 50 μm, and beneficially a thickness of 1 to 10 μm.

The repair agent of the present disclosure includes a phosphoric acid compound and a phosphonic acid compound. The repair agent is defined as an agent which forms a protective film on an exposed surface of a metal base.

The phosphoric acid compound is an inorganic phosphoric acid compound of phosphoric acid (H₃PO₄), or a phosphate, or both. For the formation of the protective film, the phosphoric acid compound beneficially is a phosphate. The phosphate is a salt of phosphoric acid ions such as first phosphoric acid ions (H₂PO₄−), second phosphoric acid ions (HPO₄ ²⁻), or third phosphoric acid ions (PO₄ ³⁻), and cations. For the formation of the protective film, it is beneficial if the phosphoric acid ions are the first and second phosphoric acid ions, and even more beneficial if the phosphate ions are the first phosphoric acid ions. The cations are one or more ions selected from a group consisting of monovalent metal ions, divalent metal ions, trivalent metal ions, and ammonium ions. Beneficially, the cations are monovalent metal ions and ammonium ions. A metal comprising the monovalent metal ions may be an alkali metal (e.g., sodium, potassium, or lithium), and beneficially is sodium and potassium. A metal comprising the divalent metal ions may be an alkaline earth metal (e.g., magnesium, calcium, strontium, or barium) or manganese, and beneficially is calcium, barium, and manganese. A metal comprising the trivalent metal ions may be, e.g., chrome or aluminum, and beneficially is chrome.

Concrete examples of the phosphoric acid compound beneficial for the formation of the protective film include: phosphoric acid (H₃PO₄), sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, calcium dihydrogen phosphate, barium dihydrogen phosphate, manganese dihydrogen phosphate, lithium dihydrogen phosphate, ammonium sodium hydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, barium hydrogen phosphate, manganese(II) hydrogen phosphate, chromium(III) phosphate, tripotassium phosphate, trisodium phosphate, and a condensed phosphoric acid compound. The condensed phosphoric acid compound may be, e.g., a compound comprised of cations and anions of tripolyphosphate, pyrophosphate, metaphosphate, or phosphorous acid. The cations are selected among alkali metal ions, alkali earth metal ions, or amphoteric metal ions (zinc ions or aluminum ions).

Examples of the phosphoric acid compound beneficial for the formation of the protective film include: sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, ammonium sodium hydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, and a condensed phosphoric acid compound. Beneficial concrete examples of the condensed phosphoric acid compound include: aluminum dihydrogen tripolyphosphate, calcium tripolyphosphate, zinc tripolyphosphate, sodium tripolyphosphate, calcium metaphosphate, calcium pyrophosphate, aluminum phosphite, and zinc phosphite.

The phosphoric acid compound is commercially available, and thus easy to obtain. As an alternative, two or more compounds may be used as the phosphoric acid compound.

As long as the phosphonic acid compound includes atoms including unshared electron pairs which contribute to adhesion of the protective film to the metal base 1, the phosphonic acid compound is not particularly limited. For example, the phosphonic acid compound may be an organic phosphonic acid compound of a nitrogen-containing phosphonic acid compound, or a salt of the nitrogen-containing phosphonic acid, or both. The organic phosphonic acid compound is a compound including an organic group and a phosphonate group. The organic group may be an alkylene group. In particular, an alkylene group with one to three carbon atoms are beneficial. The phosphonate group is represented with the formula —P(═O)(OH)₂, and may as well have the form of a salt. The phosphonate group having the form of a salt means that hydrogen ions of the hydroxyl group of the phosphonate group are liberated, and may be replaced by, e.g., metal ions. The metal ions may be, e.g., sodium ions, potassium ions, or calcium ions.

As long as the nitrogen-containing phosphonic acid compound is an organic compound including nitrogen atoms and a phosphonate group, the nitrogen-containing phosphonic acid compound is not particularly limited. The nitrogen-containing phosphonic acid compound may be an amine containing a phosphonate group of, e.g., amino tris(methylene phosphonate) (ATMP) (chemical formula: N[CH₂PO(OH)₂]₃), aminotris(ethylene phosphonate) (chemical formula: N[CH₂CH₂PO(OH)₂]₃), and their metallic salts. If the compound includes two or more hydroxyl groups in one molecule, in the metallic salts the hydrogen ions in a part of the hydroxyl groups may be replaced by metal ions. Alternatively, the hydrogen ions in all of the hydroxyl groups may be replaced by metal ions.

The phosphonic acid compound is commercially available, and thus easy to obtain. As an alternative, two or more compounds may be used as the phosphonic acid compound.

The phosphoric acid compound and the phosphonic acid compound are generally included in a weight ratio ranging from 10/90 to 90/10. For the formation of the protective film, the weight ratio beneficially ranges from 20/80 to 80/20, more beneficially from 40/60 to 80/20, and even more beneficially from 55/45 to 75/25. If two or more compounds are used as the phosphoric acid compound, it is beneficial if the total amount of these compounds falls within the above ranges. If two or more compounds are used as the phosphonic acid compound, it is beneficial if the total amount of these compounds falls within the above ranges.

Since the repair agent of the present disclosure includes a combination of the phosphoric acid compound and the phosphonic acid compound, an advantageously non-conductive and adhesive protective film can be formed on the surface of a metal base which is exposed because of a defect. As a result, it may be assumed that corrosion resistance is sufficiently improved. If a compound such as a nitrate compound, a carbonate compound, a carbonate hydrogen compound, a chromate compound, a silicate compound, a fluoride metal, or a metallic oxide is used instead of the phosphoric acid compound, or if an aromatic or aliphatic carboxylic acid, or an organic amine is used instead of the phosphonic acid compound, the protective film is not formed, or—even if the protective film is formed—the protective film declines in non-conductivity, or in adhesiveness, or in both. As a result, a sufficient corrosion resistance fails to be achieved. In the present description, non-conductivity is defined as an insulating property where volume resistivity is higher than or equal to 10¹² Ω·cm.

When the protective film is formed, the phosphoric acid ions in the phosphoric acid compound generate, due to a reaction (see, e.g., schematic chemical equation (I) below) with ions of the metal A with a strong tendency to ionization included in the plating layer, a non-conductive compound which serves as a main component for the structure of the film. On the other hand, while the phosphonic acid compound forms a complex together with ions of the metal A with a strong tendency to ionization (see, e.g., schematic chemical equation (II) below), unshared electron pairs of the nitrogen atoms included in the phosphonic acid compound make the phosphonic acid compound adhere to the surface of the metal base. In addition, this phosphonic acid compound complex promotes an amorphization of the film, and enhances flexibility and adhesiveness of the film with regard to the surface of the metal base. As a result, a protective film of a superb non-conductivity and adhesiveness is formed, and it may be assumed that corrosion resistance is sufficiently improved. Note that in the chemical equations below, formation of products derived from main materials involved in the formation of the protective film is expressed schematically.

Chemical Equation 1

Zn²⁺NaH₂PO₄→Zn₃(PO₄)₂.4H₂O  (I)

Zn²⁺+ATMP→Zn−ATMP(complex)  (II)

In this description, corrosion resistance is defined as a feature which allows for resisting corrosion, in particular the ability to resist corrosion sufficiently even in the case of a defect where a metal base is exposed. The concept of corrosion resistance includes the ability of a substance to repair itself. The ability of a substance to repair itself is a behavior where the substance repairs a defect by forming a protective film on a surface of a metal base exposed due to the defect.

To enhance the formation of the protective film, the repair agent of the present disclosure beneficially further includes a compound including a metal with a strong tendency to ionization. Hereinafter, the metal with a strong tendency to ionization which is included in such a compound included in the repair agent is distinguished from the metal A with a strong tendency to ionization included in the plating layer, and is referred to as a “metal B with a strong tendency to ionization.” The metal B with a strong tendency to ionization also contributes in ionic form to the formation of the protective film. The metal B with a strong tendency to ionization may be chosen from the same range of metals as the metal A with a strong tendency to ionization. Beneficially, the metal B with a strong tendency to ionization is the same kind of metal as the metal A with a strong tendency to ionization.

As long as the metal has an ionic form in water, the metal B with a strong tendency to ionization is not particularly limited. The metal B with a strong tendency to ionization may be, e.g., zinc, iron, magnesium, cobalt, nickel, chromium, silver, zirconium, or aluminum. Among these metals, divalent to quadrivalent (beneficially divalent and quadrivalent) metals—in particular zinc, iron, nickel, and zirconium—are beneficial, and zinc is even more beneficial, for the formation of a complex in water, in particular for the formation of a complex with ATMP. As long as the metal has an ionic form in water, the compound including the metal B with a strong tendency to ionization is not particularly limited. Beneficial examples of the compound included in the metal B with a strong tendency to ionization include, for instance, zinc sulfate, iron sulfate, nickel sulfate, zirconium sulfate, zinc nitrate, aluminum sulfate, aluminum nitrate, magnesium sulfate, and magnesium nitrate.

The compound including the metal B with a strong tendency to ionization is beneficially included at 10 to 400 parts by weight per 100 parts by weight of a total amount of the phosphoric acid compound and the phosphonic acid compound. For the formation of the protective film, the compound is particularly beneficially included at 30 to 300 parts by weight, more beneficially at 80 to 200 parts by weight, and most beneficially at 110 to 150 parts by weight. If two or more compounds are used as the compound including the metal B with a strong tendency to ionization, it is beneficial if the total amount of these compounds falls within the above ranges.

—Repair Method for Plated Base (Use of Repair Agent)—

The present disclosure further provides a method for repairing a plated base using the repair agent described above.

In the scope of the repair method for a plated base, the repair agent may be already included in the plating layer, or may be applied separately as an aqueous solution.

If the repair agent is already included in the plated layer, for instance in the scope of a mechanical plating process, the repair agent is allowed to adhere to surfaces of the constituent metal particles in the outer shells of the composite particles projected onto the object (metal base 1) subjected to mechanical plating. As a result, as shown in FIG. 2, a repair agent 30 is present between the boundary surfaces of and in the gaps between the constituent metal particles 21 included in the plating layer 2. However, the plating layer 2 shown in FIG. 2, where the repair agent 30 is indicated as black dots, is not limited to this. Alternatively, the constituent metal particles 21 may be for example present in form of a layer on the surface of the constituent metal particles 21. In such a case the repair agent is generally included at 0.15 to 18.20 wt %, and beneficially at 0.50 to 7.70 wt %, of the total amount of the plating layer.

If, in this case, the plated base 10 suffers a defect 13 reaching to the metal base 1 as the one shown in FIG. 2, the metal with a strong tendency to ionization included in the plating layer 2, the phosphoric acid compound, and the phosphonic acid compound are effused and migrate to the exposed surface of the metal base 1. As a result, a protective film 14 is formed. The metal with a strong tendency to ionization which is effused onto the exposed surface of the metal base 1 may be the metal A with a strong tendency to ionization comprising the plating layer 2. Alternatively, the metal with a strong tendency to ionization may be a mixture derived from a compound including the metal A with a strong tendency to ionization and the metal B with a strong tendency to ionization which is included in the repair agent. The effusion and migration of materials (i.e., the metal with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound) comprising the protective film 14 may be accomplished by making use of moisture (e.g., rain water) adhering to the defect 13, or by making use of moisture in the air, or by immersing the plated base 10, which has suffered the defect 13, in water.

Further, in the case where the repair agent is already included in the plating layer, for example a solution of the repair agent may be applied onto the surface of the plating layer 2 and dried such that a layer of the repair agent 30 forms on the surface of the plating layer 2, as shown in FIG. 3. In this case, although not shown in FIG. 3, the repair agent 30 may be also present at the boundary surfaces and in the gaps between the constituent metal particles 21 as shown in FIG. 2. A solvent comprising the solution is not particularly limited as long as the solvent dissolves all components of the repair agent. The solvent may be water or an organic solvent medium. In such a case, the repair agent is generally included at an amount falling within the same range as in the above-mentioned case. This allows the repair agent to be present on the boundary surfaces of and in the gaps between the constituent metal particles of the plated layer.

If, in this case, the plated base 10 suffers a defect 13 reaching to the metal base 1 as the one shown in FIG. 3, the metal with a strong tendency to ionization included in the plating layer 2, the phosphoric acid compound, and the phosphonic acid compound migrate to the exposed surface of the metal base 1. As a result, a protective film 14 is formed. The metal with a strong tendency to ionization which migrates to the exposed surface of the metal base 1, may be the metal A with a strong tendency to ionization comprising the plating layer 2. Alternatively, the metal with a strong tendency to ionization may be a mixture derived from a compound including the metal A with a strong tendency to ionization and the metal B with a strong tendency to ionization which is included in the repair agent. The migration of materials (i.e., the metal with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound) comprising the protective film 14 may be accomplished by making use of moisture (e.g., rain water) adhering to the defect 13, or by making use of moisture in the air, or by immersing the plated base 10, which has suffered the defect 13, in water.

In the case where the repair agent is used separately from the plated base in the form of an aqueous solution, when the plated base suffers a defect reaching to its metal base, an aqueous solution 31 of the repair agent comes into contact with the defect 13 as shown in FIG. 4. As a result, the metal A with a strong tendency to ionization included in the plating layer 2 is effused onto the exposed surface of the metal base. In this case, the phosphoric acid compound and the phosphonic acid compound which are included in the repair agent dissolved in the aqueous solution, and, if desired, also the metal B with a strong tendency to ionization migrate to the exposed surface of the metal base. As a result, the metal with a strong tendency to ionization, the phosphoric acid compound and the phosphonic acid compound form a protective film on the exposed surface of the metal base. The effusion and migration of materials (i.e., the metals A and B with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound) comprising the protective film 14 is accomplished by making use of the migration of these materials within the aqueous solution of the repair agent. Although the repair agent 30 is indicated as black dots dispersed in the aqueous solution 31 shown in FIG. 4, in general, the repair agent 30 is dissolved in the aqueous solution.

In FIG. 4, the aqueous solution 31 of the repair agent is brought into contact with the defect 13 by applying the aqueous solution 31 of the repair agent onto the defect 13. Alternatively, however, the aqueous solution 31 of the repair agent may be brought into contact with the defect 13 by, for example, immersing the plated base which has suffered the defect in the aqueous solution of the repair agent.

In this case, the concentration (total concentration of all components) of the repair agent in the aqueous solution is higher than or equal to 100 ppm, in particular higher than or equal to 500 ppm. Beneficially the concentration ranges from 500 to 10000 ppm (inclusive), and even more beneficially from 800 to 10000 ppm (inclusive). Here, “ppm” is an entity indicating a proportion by weight base.

In the scope of the repair method for the plated base of the present disclosure, the protective film 14 is selectively formed on the exposed surface of the metal base 1. This method is not bound to any specific theory but is employed for the following reasons:

(1) In an initial state the metal base 1 has a corrosion potential (negative), which is why, when the metal with a strong tendency to ionization is electrostatically pulled as cations toward the exposed surface of the metal base 1, other constituent materials of the protective film are electrostatically pulled toward the cations.

(2) After having adhered to the surface of the metal base 1, the ions which have been pulled toward the exposed surface bond together and form a film. While forming a two- or three-dimensional film, the ions are strongly absorbed into or strongly bonded to the surface of the metal base 1, and become a strongly adhesive film.

The fact that the protective film 14 has been formed on the exposed surface of the metal base 1 can be easily verified by taking an SEM photograph of the surface, or by performing an X-ray diffraction analysis (XRDA) of the film on the surface.

In the present description, the defect 13 is a scratch so deep that it reaches from the surface of the plated base 2 to the metal base 1.

EXAMPLES Experimental Example A Example A1

In a device 50 which is shown in FIG. 5, a carbon steel sheet (high-tensile material; 12 mm×12 mm; content proportions: 0.5 wt % carbon, 0.02 wt % silicon, 0.2 wt % manganese, 0.1 wt % phosphorus, 0.1 wt % sulfur, and iron (remainder)) has been used as a working electrode 51, and immersed for 24 h in a test fluid 52 (35° C.) saturated with air. Then a spontaneous potential has been measured. The test fluid has been prepared by dissolving sodium dihydrogen phosphate, ATMP, and zinc sulfate, which serve as the repair agent, in a sodium chloride aqueous solution. The concentration of sodium chloride was 0.5 wt %, the concentrations of sodium dihydrogen phosphate, ATMP, and zinc sulfate were 500 ppm each. The pH level of the test fluid was adjusted to 6.2 with the aid of NaOH/HCl. A platinum electrode has been employed as a counter electrode 53, and an Ag/AgCl electrode has been employed as a reference electrode 54.

Subsequently, while keeping the working electrode 51 immersed in the test fluid 52, the potential of the working electrode 51 has been altered using a potentiostat 55. Simultaneously, cathodic polarization has been performed at the working electrode 51 and cathodic current values have been determined. One example of a current-potential curve obtained this way is shown in FIG. 6. In FIG. 6, the current-potential curve of Example A1 is expressed as “ATMP+NaH₂PO₄+ZnSO₄.” In FIG. 6, a current reduction rate E has been calculated at current values of −0.8 V and −1.1 V.

The current reduction rate E has been calculated based on the below equation.

E (%)=(I _(o) −I)/I _(o)×100  Equation (1)

In the above equation, I_(o) is current density when no repair agent has been added to the test fluid. Specifically, I_(o) is the current density when no repair agent has been added in the scope of Comparative Example A1 which will be described later.

In the equation, I is the current density when the repair agent of Example A1 is added to the test fluid. Further, I is the current density measured in this example.

The cathodic current value decreasing due to the addition of the repair agent means that the protective film has been formed on the exposed surface of the metal base, and indicates that the repair agent features corrosion resistance and, in particular, can repair itself.

Comparative Examples A1 to A34

In Comparative Examples A1 to A34, except for having dissolved a predetermined amount of a predetermined compound in a test fluid, the cathodic current value has been determined and the current reduction rate E has been calculated in the same manner as in Example A1. Kinds and amounts of the compounds of each of the Comparative Examples have been listed in the below table. Potentials for determining the current reduction rate have been −0.8 V and −1.1 V. In FIG. 6, the current-potential curve of Comparative Example A1 is indicated as “Plain,” the current-potential curve of Comparative Example A5 as “NaH₂PO₄,” the current-potential curve of Comparative Example A6 as “ZnSO₄,” and the current-potential curve of Comparative Example A26 as “ATMP.”

TABLE 1 Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative ative ative ative Example Example Example Example Example Example Example Example Example Example A1 A1 A2 A3 A4 A5 A6 A7 A8 A9 Sodium 500 ppm — — — — 500 ppm — — — — Dihydrogen Phosphoric Acid Sodium — — — — 500 ppm — — — — — Nitrate Sodium — — — — — — — 500 ppm — — Bicarbonate Sodium — — — — — — — — 500 ppm — Fluoride Colloidal — — — — — — — — — 500 ppm Silicon Dioxide Vanadium — — — — — — — — — — Oxide Potassium — — — — — — — — — — Chromate Sodium — — — — — — — — — — Silicate ATMP 500 ppm — — — — — — — — — Sodium — — 500 ppm — — — — — — — Benzoate Sodium — — — — — — — — — — Oleate Ethyl Amine — — — 250 ppm — — — — — — Zinc Sulfate 500 ppm — — — — — 500 ppm — — — E (−0.8 V) (%) 81 (1) 7 39 27 19 0 44 −15 46 E (−1.1 V) (%) 80 (1) 13 −2 −125 39 −34 −52 −55 31 The number (1) indicates reference values. The m-dash (“—”) indicates that the respective compound has not been used.

TABLE 2 Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative ative ative ative ative Example Example Example Example Example Example Example Example Example Example A10 A11 A12 A13 A14 A15 A16 A17 A18 A19 Sodium — 500 ppm — — — — — — 500 ppm — Dihydrogen Phosphoric Acid Sodium — — 500 ppm — — — — — — — Nitrate Sodium — — — — 500 ppm — — 1000 ppm — — Bicarbonate Sodium — — — 500 ppm — — — — — — Fluoride Colloidal — — — — — — — — — — Silicon Dioxide Vanadium 500 ppm — — — — — — — — — Oxide Potassium — — — — — — — — — — Chromate Sodium — — — — — — — — — — Silicate ATMP — — — — — — — — — — Sodium — — — — — — — — — — Benzoate Sodium — — — — — — — — — — Oleate Ethyl Amine — 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 1000 ppm — — — Zinc Sulfate — — — — — — — — 500 ppm 500 ppm E (−0.8 V) (%) −66 30 10 −75 11 −16 19 30 48 50 E (−1.1 V) (%) 0 29 −107 −68 8 −37 −40 49 82 62 The m-dash (“—”) indicates that the respective compound has not been used.

TABLE 3 Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative ative ative ative Example Example Example Example Example Example Example Example Example Example A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 Sodium — — 500 ppm 500 ppm 500 ppm — — — — — Dihydrogen Phosphoric Acid Sodium — — — — — — — — — — Nitrate Sodium — — — — — — — — — — Bicarbonate Sodium — — — — — — — — — — Fluoride Colloidal — — 500 ppm 500 ppm 500 ppm — — 500 ppm — — Silicon Dioxide Vanadium — — 500 ppm 500 ppm — — — — — — Oxide Potassium 500 ppm 500 ppm — — — — — — — 1000 ppm Chromate Sodium — — — — — — — — — — Silicate ATMP — — — — — — 500 ppm 500 ppm 500 ppm — Sodium — — — — — — — — — — Benzoate Sodium — — — — — 500 ppm — — — — Oleate Ethyl Amine — — — — — — — — — — Zinc Sulfate — 500 ppm 500 ppm — 500 ppm — — — 500 ppm — E (−0.8 V) (%) 36 61 10 8 26 −44 22 −21 49 −38 E (−1.1 V) (%) 10 24 40 33 74 53 9 4 76 42 The m-dash (“—”) indicates that the respective compound has not been used.

TABLE 4 Comparative Comparative Comparative Comparative Comparative Example Example Example Example Example A30 A31 A32 A33 A34 Sodium Dihydrogen — — 500 ppm 500 ppm — Phosphoric Acid Sodium Nitrate — — — — — Sodium Bicarbonate — — — — — Sodium Fluoride — — — — — Colloidal Silicon Dioxide — 500 ppm 500 ppm 500 ppm — Vanadium Oxide — — — — — Potassium Chromate — — — — 500 ppm Sodium Silicate 500 ppm 500 ppm 500 ppm 500 ppm — ATMP — — — — — Sodium Benzoate — — — — — Sodium Oleate — — — — 500 ppm Ethyl Amine — — — — — Zinc Sulfate — — — 500 ppm — E (−0.8 V) (%) −30 −45 45 29 62 E (−1.1 V) (%) −24 9 62 50 61 The m-dash (“—”) indicates that the respective compound has not been used.

In the scope of Example A1 and Comparative Examples A1, A18, A24, and A28, SEM photographs of surfaces of working electrodes have been taken after determination of cathodic current values. The SEM photographs are shown in FIGS. 7 to 11. An SEM photograph of the surface of a working electrode before immersion into the test fluid is shown in FIG. 12.

Results of these examples have shown that by forming a protective film with an excellent adhesiveness on a surface of a metal base, the repair agent of the present disclosure allows for forming of a protective film with an excellent cathodic current reduction rate, i.e., a protective film excellent in reducing oxygen and hydrogen reduction reactions.

Example A2

In Example A2, apart from having set the concentration of sodium chloride in the test fluid to 3.5 wt %, cathodic polarization has been performed in the same manner as in Example A1. After cathodic polarization, the protective film on the surface of the working electrode has been subjected to thermogravimetric analysis (TGA). Analysis results are shown in FIG. 13.

Comparative Example A35

In Comparative Example A35, except for having set the concentration of sodium chloride in the test fluid to 3.5 wt %, cathodic polarization has been performed in the same manner as in Example A18. After cathodic polarization, the protective film on the surface of the working electrode has been subjected to thermogravimetric analysis (TGA). Analysis results are shown in FIG. 13.

Experimental Example B Examples B1 to B10 and Comparative Examples B1 to B6

In Examples B1 to B10 and Comparative Examples B1 to B6, except for having dissolved a predetermined amount of a predetermined compound in a test fluid, the cathodic current values have been determined and the current reduction rate E has been calculated in the same manner as in Example A1. Kinds and amounts of the compounds of each of the Examples and each of the Comparative Examples have been listed in the below table.

The current reduction rates E have been ranked in the following manner.

−0.8 V

S: E≧85%;

A: E≧80%;

B: E≧75%;

C: E≧70% (unproblematic in practical use);

D: E<70% (problematic in practical use).

−1.2 V

S: E≧91%;

A: E≧88%;

B: E≧85%;

C: E≧76% (unproblematic in practical use);

D: E<70% (problematic in practical use).

TABLE 5 Example Example Example Example Example Example Example Example Example Example B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 Sodium 30 25 15 15 20 40 50 33.3 40 25 Dihydrogen Phosphate (wt %) (2) ATMP (wt %) (2) 15 25 30 15 40 20 25 33.3 40 50 Zinc Sulfate 55 50 55 70 40 40 25 33.4 20 25 (wt %) (2) Sodium 67:33 50:50 33:67 50:50 33:67 67:33 67:33 50:50 50:50 33:67 Dihydrogen Phosphate:ATMP Zinc 122/100 100/100 122/100 233/100 67/100 67/100 33/100 50/100 25/100 33/100 Sulfate/(Sodium Dihydrogen Phosphate + ATMP) E (−0.8 V) (%) S A B B B C C C C C E (−1.2 V) (%) S S A B C B B B C B (2) Each amount is the proportion with regard to a total amount of sodium dihydrogen phosphate, ATMP, and zinc sulfate. The total amount has been implemented as 1000 ppm.

TABLE 6 Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative Example Example Example Example Example Example B1 B2 B3 B4 B5 B6 Sodium 100 — — 50 — 50 Dihydrogen Phosphate (wt %) (2) ATMP — 100 — — 50 50 (wt %) (2) Zinc Sulfate — — 100 50 50 — (wt %) (2) Sodium 100:0 0:100 0:0 50:0 0:50 50:50 Dihydrogen Phosphate:ATMP Zinc 0/100 0/100 100/0 50/50 50/50 0/100 Sulfate/(Sodium Dihydrogen Phosphate + ATMP) E (−0.8 V) (%) D D D D D D E (−1.2 V) (%) D D D D D D (2) Each amount is the proportion with regard to a total amount of sodium dihydrogen phosphate, ATMP, and zinc sulfate. The total amount has been implemented as 1000 ppm. The m-dash (“—”) indicates that the respective compound has not been used.

In Comparative Example B4, an SEM photograph of a surface of a working electrode after determination of cathodic current values has been taken, and shown in FIG. 14. Further, in Example B1 and Comparative Example B4, the protective films formed on the surfaces of the working electrodes has been subjected to X-ray diffraction analysis (XRDA). Analysis results are shown in FIG. 15. Analysis results lead to the conclusion that addition of ATMP eliminates peaks of Zn₃(PO₄)₂.4H₂O and promotes formation of amorphous structures.

Experimental Example C: Method for Determining Current when Measuring Current Reduction Rate E Reference Example C1

In Reference Example C1, except for having saturated the test fluid with nitrogen instead of air, cathodic current values have been determined and a current-potential curve has been obtained in the same manner as in Comparative Example A1. In FIG. 16, the current-potential curve of Reference Example C1 is indicated as “N₂,” and the current-potential curve of Comparative Example A1 as “Air.” Since the experiment results show that oxygen reduction reactions predominantly occur at a potential around −0.8 V, and hydrogen reduction reactions predominantly occur at a potential around −1.1 V, potentials when the current reduction rate E is calculated have been determined as values close to each of these potentials. 

What is claimed is:
 1. A repair agent for a plated base including a plating layer which is disposed on a surface of a metal base and which includes a metal with a stronger tendency to ionization than metal comprising the metal base, the repair agent comprising a phosphoric acid compound and a phosphonic acid compound.
 2. The repair agent of claim 1, wherein the plated base has a defect reaching to the metal base, and the metal with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound form a protective film on the surface of the metal base which is exposed where the plated base has the defect.
 3. The repair agent of claim 1, the repair agent further comprising: a compound including the metal with a strong tendency to ionization.
 4. The repair agent of claim 3, wherein the metal with a strong tendency to ionization included in the compound also contributes to formation of the protective film.
 5. The repair agent of claim 3, wherein the repair agent includes the compound including the metal with a strong tendency to ionization at 10 to 400 parts by weight with respect to the phosphoric acid compound and the phosphonic acid compound included in total at 100 parts by weight.
 6. The repair agent of claim 1, wherein the phosphoric acid compound is an inorganic phosphoric acid compound.
 7. The repair agent of claim 6, wherein the inorganic phosphoric acid compound is a compound of a phosphoric acid (H₃PO₄), or a phosphate, or both.
 8. The repair agent of claim 7, wherein the phosphate is a salt of first phosphoric acid ions (H₂PO₄ ⁻), second phosphoric acid ions (HPO₄ ²⁻), or third phosphoric acid ions (PO₄ ³⁻), and cations, and the cations are one or more ions selected from a group consisting of monovalent metal ions, divalent metal ions, trivalent metal ions, and ammonium ions.
 9. The repair agent of claim 1, wherein the phosphonic acid compound is an organic phosphonic acid compound.
 10. The repair agent of claim 9, wherein the organic phosphonic acid compound is a compound of a nitrogen-containing phosphonic acid compound, or a salt of the nitrogen-containing phosphonic acid, or both.
 11. The repair agent of claim 10, wherein the nitrogen-containing phosphonic acid compound is an amine which includes a phosphonate group.
 12. The repair agent of claim 1, wherein the metal with a strong tendency to ionization is one or more metals selected from a group consisting of zinc, aluminum, and magnesium.
 13. The repair agent of claim 1, wherein the plating layer is a zinc plating layer.
 14. A method for repairing the plated base using the repair agent of claim
 1. 15. The method of claim 14, wherein the repair agent is already included in the plating layer, and when the plated base suffers a defect reaching to the metal base, the metal with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound which are included in the plating layer form a protective film on the surface of the metal base which is exposed where the plated base has the defect.
 16. The method of claim 14, wherein when the plated base suffers a defect reaching to the metal base, while an aqueous solution of the repair agent is brought into contact with the defect, the metal with a strong tendency to ionization included in the plating layer is effused onto the surface of the metal base which is exposed where the plated base has the defect, and the metal with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound form a protective film on the surface of the metal base exposed.
 17. The method of claim 16, wherein the repair agent is brought into contact with the defect by applying the aqueous solution of the repair agent onto the defect, or by immersing the plated base which has the defect in the aqueous solution of the repair agent.
 18. A plated base comprising: a plating layer which is disposed on a surface of a metal base and which includes a metal with a stronger tendency to ionization than a metal included in the metal base and a repair agent, wherein the repair agent includes a phosphoric acid compound and a phosphonic acid compound.
 19. The plated base of claim 18, wherein the repair agent further includes a compound which includes the metal with a strong tendency to ionization.
 20. The plated base of claim 19, wherein the plated base includes the compound including the metal with a strong tendency to ionization at 10 to 400 parts by weight with respect to the phosphoric acid compound and the phosphonic acid compound included in total at 100 parts by weight. 